Propelled by relentless ocean waves and strong onshore winds, small grains of sand accumulated to form the impressive dunes of Guadalupe-Nipomo Dunes National Wildlife Refuge in California. Stretching inland from the Pacific Ocean, the migrating dunes are home to a unique ecosystem of plants and animals, like the northern elephant seal, the western snowy plover and the California red-legged frog. Two remote hiking areas offer visitors a chance to explore this dynamic landscape in peace and solitude. Photo by Ian Shive, U.S. Fish and Wildlife Service. Posted on Tumblr by the US Department of the Interior, 7/5/17.